The present invention relates to a thermal expansion valve used in a refrigeration cycle.
Conventionally, a thermal expansion valve shown in FIG. 5 is used in a refrigeration cycle in order to control the flow rate of the refrigerant being supplied to an evaporator and to decompress the refrigerant.
In FIG. 5, a prism-shaped aluminum valve body 510 comprises a first refrigerant passage 514 including an orifice 516, and a second refrigerant passage 519, the two passeges formed mutually independent from one another. One end of the first refrigerant passage 514 is communicated to the entrance of an evaporator 515, and the exit of the evaporator 515 is communicated through the second refrigerant passage 519, a compressor 511, a condenser 512 and a receiver 513 to the other end of the first refrigerant passage 514. A bias means 517 which is a bias spring biasing a sphere-shaped valve means 518 is formed to a valve chamber 524 communicated to the first refrigerant passage 514, and the valve means 518 is driven toward or away from the orifice 516. Further, the valve chamber 524 is sealed by a plug 525, and the valve means 518 is biased through a support member 526. A power element 520 including a diaphragm 522 is fixed to the valve body 510 adjacent to the second refrigerant passage 519. An upper chamber 520a in the power element 520 defined by the diaphragm 522 is maintained airtight, and is filled with temperature-corresponding working fluid.
A small pipe 521 extending out from the upper chamber 520a of the power element 520 is used to degasify the upper chamber 520a and to fill the temperature-corresponding working fluid to the upper chamber 520a, before the end of the pipe is sealed. The extended end of a valve drive member 523 functioning as the heat-sensing/transmitting member positioned within the valve body 510 extending from the valve means 518 and penetrating through the second refrigerant passage 519 is positioned in the lower chamber 520b of the power element 520, contacting the diaphragm 522. The valve drive member 523 is made of a material having a large thermal capacity, and it transmits the temperature of the refrigerant vapor exiting the evaporator 515 and flowing through the second refrigerant passage 519 to the temperature-corresponding working fluid filling the upper chamber 520a of the power element 520, which generates a working gas having a pressure corresponding to the transmitted temperature. The lower chamber 520b is communicated to the second refrigerant passage 519 through the space formed around the valve drive member 523 within the valve body 510.
Accordingly, the diaphragm 522 of the power element 520 uses the valve drive member 523 to adjust the valve opening of the valve means 518 against the orifice 516 (that is, the amount of flow of liquid-phase refrigerant entering the evaporator) according to the difference in pressure of the working gas of the temperature-corresponding working fluid filling the upper chamber 520a and the pressure of the refrigerant vapor exiting the evaporator 515 in the lower chamber 520b, under the influence of the biasing force of the bias means 517 provided to the valve means 518.
According to the above-mentioned prior-art thermal expansion valve, the power element 520 is exposed to external atmosphere, and the temperature-corresponding driving fluid in the upper chamber 520a receives influence not only from the temperature of the refrigerant exiting the evaporator and transmitted by the valve drive member 423 but also from the external atmosphere, especially the engine room temperature. Moreover, the above conventional valve structure often causes a so-called hunting phenomenon where the valve responds too sensitively to the refrigerant temperature at the exit of the evaporator and repeats the opening and closing movement of the valve means 518. The hunting phenomenon is caused for example by the structure of the evaporator, the way the pipes of the refrigeration cycle are positioned, the way the expansion valve is used, and the balance with the heat load.
Conventionally, a time constant retardant such as an absorbent or a thermal ballast is utilized to suppress such hunting phenomenon. FIG. 6 is a cross-sectional view showing the conventional thermal expansion valve utilizing an activated carbon as an adsorbent, the structure of which is basically similar to the prior-art thermal expansion valve of FIG. 5, except for the structure of the diaphragm and the structure of the valve drive member that functions as a heat-sensing driven member. According to FIG. 6, the thermal expansion valve comprises a prism-shaped valve body 50, and the valve body 50 comprises a port 52 through which the liquid-phase refrigerant flowing through a condenser 512 and entering from a receiver tank 513 travels into a first passage 62, a port 58 sending the refrigerant traveling through the first passage 62 out toward an evaporator 515, an entrance port 60 of a second passage 63 through which the gas-phase refrigerant exiting the evaporator returns, and an exit port 64 through which the refrigerant exits toward the compressor 511.
The port 52 through which the refrigerant is introduced is communicated to a valve chamber 54 positioned on the center axis of the valve body 50, and the valve chamber 54 is sealed by a nut-type plug 130. The valve chamber 54 is communicated through an orifice 78 to a port 58 through which the refrigerant exits toward the evaporator, 515. A sphere-shaped valve means 120 is mounted to the end of a small-diameter shaft 114 that penetrates the orifice 78, and the valve means 120 is supported by a support member 122. The support member 122 biases the valve means 120 toward the orifice 78 using a bias spring 124. The area of the flow path for the refrigerant is adjusted by varying the gap formed between the valve means 120 and the orifice 78. The refrigerant sent out from the receiver 514 expands while passing through the orifice 78, and travels through the first passage 62 and exits from the port 58 toward the evaporator. The refrigerant exiting the evaporator enters from the port 60, and travels through the second passage 63 and exits from the port 64 toward the compressor.
The valve body 50 is equipped with a first hole 70 formed from the upper end portion along the axis, and a power element portion 80 is mounted to the first hole using a screw portion and the like. The power element portion 80 includes housings 81 and 91 that constitute the heat sensing portion, and a diaphragm 82 that is sandwiched between these housings and fixed thereto through welding. The upper end portion of a heat-sensing driven member 100 made of stainless steel or aluminum is welded onto a round hole or opening formed to the center area of the diaphragm 82 together with a diaphragm support member 82xe2x80x2. The diaphragm support member 82xe2x80x2 is supported by the housing 81.
An inert gas is filled inside the housing 81, 91 as a temperature-corresponding working fluid, which is sealed thereto by the small tube 21. Further, a plug body welded to the housing 91 can be used instead of the small tube 21. The diaphragm 82 divides the space within the housing 81, 91 forming an upper chamber 83 and a lower chamber 85.
The heat-sensing driven member 100 is formed of a hollow pipe-like member exposed to the second passage 63, with activated carbon 40 stored to the interior thereof. The upper end of the heat-sensing/pressure transmitting member 100 is communicated to the upper chamber 83, defining a pressure space 83a by the upper chamber 83 and the hollow portion 84 of the heat-sensing driven member 100. The pipe-like heat-sensing driven member 100 penetrates through a second hole 72 formed along the axis of the valve body 50, and is inserted to a third hole 74. A gap is formed between the second hole 72 and the heat-sensing driven member 100, through which the refrigerant in the passage 63 is introduced to the lower chamber 85 of the diaphragm.
The heat-sensing driven member 100 is slidably inserted to the third hole 74, and the end thereof is connected to one end of the shaft 114. The shaft 114 is slidably inserted to a fourth hole 76 formed to the valve body 50, and the other end thereof is connected to the valve means 120.
According to this structure, the adsorbent 40 functioning as a time constant retardant works as follows. When a granular activated carbon is used as the adsorbent 40, the combination of the temperature-corresponding working fluid and the adsorbent 40 is an absorption-equilibrium type, where the pressure can be approximated by a linear expression of the temperature within a considerably wide temperature range, and the coefficient of the linear expression can be set freely according to the amount of granular activated carbon used as the adsorbent. Therefore, the character of the thermal expansion valve can be set at will.
Accordingly, it takes a relatively long time to set the adsorption-equilibrium-type pressure-temperature equilibrium state when the temperature of the refrigerant vapor flowing out from the exit of the evaporator 515 is either rising or falling. In other words, by increasing the time constant, the work efficiency of the air conditioning device is improved, stabilizing the performance of the air conditioning device capable of suppressing the sensitive operation of the thermal expansion valve caused by the influence of disturbance which may lead to the hunting phenomenon.
However, the hunting phenomenon differs according to the characteristic of each individual refrigeration cycle. Especially when a fine temperature variation occurs to the low-pressure refrigerant exiting the evaporator, the small fluctuation or pulsation of the refrigerant temperature is transmitted directly to the opening/closing movement of the valve means, which causes unstable valve movement, and the use of a thermal ballast material or an adsorbent can no longer suppress hunting.
Therefore, the present invention aims at providing a thermal expansion valve that is capable of controlling stably the amount of low-pressure refrigerant sent out toward the evaporator, and that enables to further suppress the hunting phenomenon by providing,an appropriate delay to the response of the valve to temperature change, even when small temperature variation occurs to the low-pressure refrigerant transmitted from the evaporator. This is realized without changing the basic design of the conventional thermal expansion valve, maintaining the conventional operation of the valve.
In order to achieve the above objects, the present invention provides a thermal expansion valve including a refrigerant passage extending from an evaporator to a compressor, and a heat-sensing driven member with a hollow portion formed to the interior thereof and having a heat sensing function positioned within the refrigerant passage: wherein the end of the hollow portion of the heat-sensing,driven member is fixed to the center opening portion of a diaphragm constituting a power element portion that drives the driven member, thereby communicating the hollow portion with an upper pressure chamber defined by the diaphragm within the power element portion and forming a sealed space filled with working fluid; and
a heat transmission retardant member is placed between a time constant retardant stored within the hollow portion and the inner wall of the hollow portion so that a space is formed between the inner wall and the heat transmission retardant member.
In a preferred embodiment, the heat transmission member is cylindrical.
According to the thermal expansion valve of the present invention having a structure as explained above, a member that delays heat transmission is placed between the inner wall of the hollow portion of the heat-sensing driven member and the time constant retardants stored within the hollow portion. According to this structure, heat transmission from the heat-sensing driven member to the time constant retardant is delayed, and the time constant is increased compared to the valve where only a time constant retardant is used. In addition thereto, since a space is formed between the heat-sensing driven member and the heat transmission retardant member, the change in refrigerant temperature is transmitted with even further delay to the heat transmission retardant member. As a result, the present invention suppresses hunting of the valve member in a thermal expansion valve more effectively.
Further, the cylindrical member has protrusions formed thereto, and by contacting the protrusions to the inner wall, the space is formed between the inner wall and the cylindrical member that delays the heat transmission.
In another embodiment, the cylindrical member is formed to have a polygonal shape, the corners of which contact the inner wall so as to form the space. The present embodiment enables to form a space between the inner wall and the cylindrical member easily, and to provide further delay to the heat transmission to the heat transmission retardant member.
Moreover, the cylindrical heat transmission retardant member is preferably formed using resin material, which has sufficiently low thermal conductivity compared to stainless steel or aluminum, that is mounted between the time constant retardant and the inner wall of the hollow portion of the heat-sensing driven member.